You said,
You cannot figure it like that. You have to figure based on WHERE the piston is in the bore. You have more square inches at BDC, than TDC, get it? It's three dimensional, not one.
90 psi on a 3.91 bore makes no difference on force on piston if it 1" away from top or 20" away from top. It's still 90 psi on a 3.91" bore. Now if you are talking reality on the piston making pressure it depends on when the intake valve closes and the stroke from that point.
